Enhanced hierarchical virtual private local area network service (VPLS) system and method for Ethernet-Tree (E-Tree) services

ABSTRACT

A network apparatus comprising a trunk end point associated with an Ethernet-tree (E-Tree) service in a network domain and configured to forward a frame that comprises a tag according to the tag in the frame, wherein the tag in the frame is a root tag that indicates a root source of the frame or a leaf tag that indicates a leaf source of the frame, and wherein the trunk end point is coupled to a second end point associated with the E-tree service outside the network domain.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/258,302, filed Apr. 22, 2014, by Lucy Yong and entitled“Enhanced Hierarchical Virtual Private Local Area Network Service (VPLS)System and Method For Ethernet-Tree (E-Tree) Services,” which is acontinuation of U.S. patent application Ser. No. 12/983,605, filed Jan.3, 2011 by Lucy Yong and entitled “Enhanced Hierarchical Virtual PrivateLocal Area Network Service (VPLS) System and Method For Ethernet-Tree(E-Tree) Services,” which claims priority to U.S. Provisional PatentApplication No. 61/292,441, filed Jan. 5, 2010 by Lucy Yong and entitled“Enhanced Hierarchical VPLS System and Method for E-Tree Services,” U.S.Provisional Patent Application No. 61/305,428, filed Feb. 17, 2010 byLucy Yong and entitled “E-Tree Service Interworking Across Multiple MENand MPLS Networks,” and U.S. Provisional Patent Application No.61/367,741, filed Jul. 26, 2010 by Lucy Yong and entitled “VirtualPrivate Local Area Network Service (VPLS) Extension and LabelDistributed Protocol Extension for VPLS in Supporting Ethernet(E)-Tree,” all of which are incorporated herein by reference as ifreproduced in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Ethernet is the preferred protocol for many types of networks because itis flexible, decentralized, and scalable. Ethernet comprises a family offrame-based computer networking technologies for local area networks(LANs), and defines a number of wiring and signaling standards for thePhysical Layer of the Open Systems Interconnection (OSI) networkingmodel and a common addressing format and Media Access Control (MAC) atthe Data Link Layer. Ethernet is flexible in that it allowsvariable-sized data frames to be transported across different types ofmediums using various nodes each having different transmission speeds.Some Ethernet based networks may forward the data frames from one nodeto another node across the network along pre-configured orpre-established paths. In such cases, the nodes may create Ethernet-LAN(E-LAN) services, where traffic that corresponds to different servicesmay be transported along different sub-networks, e.g. by differentsubsets of nodes. For example, the E-LAN services may comprise theInstitute of Electrical and Electronics Engineers (IEEE) 802.1aq networkservices or Virtual Private LAN Services (VPLSs).

SUMMARY

In one embodiment, the disclosure includes a network apparatuscomprising a trunk end point associated with an Ethernet-tree (E-Tree)service in a network domain and configured to forward a frame thatcomprises a tag according to the tag in the frame, wherein the tag inthe frame is a root tag that indicates a root source of the frame or aleaf tag that indicates a leaf source of the frame, and wherein thetrunk end point is coupled to a second end point associated with theE-tree service outside the network domain and performs tag translationwhen sending a frame.

In another embodiment, the disclosure includes a network componentcomprising a receiver unit configured to receive a frame on an E-LANservice in a network domain, a circuit logic configured to detect a tagin the frame and perform a tag translation if the tag is a root tag or aleaf tag, and a transmitter unit configured to forward the frame on theE-LAN service according to the tag translation.

In yet another embodiment, the disclosure includes a system comprisingtwo VPLS provider edges (PEs) with a virtual switching instance (VSI) ineach of them inter-connected via a pseudowire (PW), wherein both VPLSPEs are attached to roots and leaves; at the PE where a frame exits thePW, if a frame with the remote virtual LAN (VLAN) leaf tag is received,then it is mapped to the local VLAN leaf tag, otherwise, if a frame withthe remote VLAN root tag is received, then it is mapped to the localVLAN root tag, wherein packets over both VLANs are processed in the samecustomer MAC space and are further forwarded or dropped in the exitbridge module using the mechanism as described in IEEE 802.1Q.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a schematic diagram of an embodiment of an E-Tree service.

FIG. 2 is a schematic diagram of an embodiment of a VPLS.

FIG. 3 is a schematic diagram of an embodiment of a VPLS based E-Tree.

FIG. 4 is a schematic diagram of an embodiment of an E-Tree serviceacross a plurality of network domains.

FIG. 5 is a schematic diagram of another embodiment of an E-Tree serviceacross a plurality of network domains.

FIG. 6 is a schematic diagram of another embodiment of an E-Tree serviceacross a plurality of network domains.

FIG. 7 is a schematic diagram of an embodiment of a Hierarchical VPLS(H-VPLS) configuration.

FIG. 8 is a schematic diagram of another embodiment of an H-VPLSconfiguration.

FIG. 9 is a schematic diagram of an embodiment of a capability parameterType-Length-Value (TLV).

FIG. 10 is a schematic diagram of an embodiment of a forward errorcorrection (FEC) TLV.

FIG. 11 is a schematic diagram of an embodiment of a generic label TLV.

FIG. 12 is a schematic diagram of an embodiment of a multi label TLV.

FIG. 13 is a flowchart of an embodiment of a frame service forwardingmethod.

FIG. 14 is a schematic diagram of an embodiment of atransmitter/receiver unit.

FIG. 15 is a schematic diagram of an embodiment of a general-purposecomputer system.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

An E-Tree service is an Ethernet service defined by the Metro EthernetForum (MEF). The E-Tree service may be implemented for a plurality ofapplications in a network, where data may be exchanged in the form ofEthernet frames and forwarded according to MAC addresses. Two types ofports are defined in the E-Tree service: root ports and leaf ports; andeach port may be located at a plurality of nodes in the network. Theroot ports and leaf ports may exchange unicast, multicast, and/orbroadcast frames, where data frames from a root port may be forwarded toother root ports and/or leaf ports. However, leaf-to-leaf communicationsare not allowed in an E-Tree service. Accordingly, data frames from aleaf port may only be forwarded to the root ports, but not to other leafports. To help prevent leaf-to-leaf communications, IEEE has defined anasymmetric VLAN across learning in which the E-Tree service may beimplemented by IEEE 802.1Q using two VLAN tags to distinguish betweenthe data forwarded from root ports and data forwarded from leaf ports.

FIG. 1 illustrates an embodiment of an E-Tree service 100 in an Ethernetbridged network domain 110. The Ethernet bridged network domain 110 maybe one of a plurality of domains in an Ethernet bridged network. TheE-Tree service 100 may be based on IEEE 802.1Q, and the Ethernet bridgednetwork domain 110 may correspond to a Metropolitan Ethernet Network(MEN). The Ethernet bridged network domain 110 may comprise a pluralityof edge nodes, e.g. PEs, that comprise a plurality of ports. At leastsome of the ports may be associated with the E-Tree service 100, whereeach of the ports may be configured as a root port 112 or a leaf port114 but not both. The root ports 112 and the leaf ports 114 in the PEsmay exchange data frames with other PEs in the Ethernet bridged networkdomain 110 using the E-Tree service 100 and possibly with other nodesexternal to the Ethernet bridged network domain 110 (not shown). A rootport 112 or a leaf port 114 in a PE also may be coupled to a customersite 120 and exchange data with the customer site 120.

According to the E-Tree service rules, the root ports 112 may forwardthe data frames to other root ports 112, to the leaf ports 114, or both.However, the leaf ports 114 may only forward the data frames to the rootports 112, not the other leaf ports 114. To forward the data framesproperly according to such rules, the data frames forwarded from theroot ports 112 and leaf ports 114 may be differentiated using differenttags. As such, the data frames forwarded from the root ports 112(indicated by solid arrow lines) may be associated with a root tag, andthe data frames forwarded from the leaf ports 114 (indicated by a dashedarrow line) may be associated with a leaf tag. The root ports 112 andleaf ports 114 may add the root tags and the leaf tags, respectively, todata frames received from external nodes, and then forward the dataframes inside the Ethernet bridged network domain 110. The root ports112 and the leaf ports 114 also may remove the root tags and the leaftags, respectively, from data frames received inside the Ethernetbridged network domain 110, and then forward the data frames to externalnodes, e.g. to the customer site 120. The data frames may be forwardedusing the E-Tree service 100 in the Ethernet bridged network domain 110according to standard Ethernet frame forwarding rules, e.g. using MACbased forwarding, broadcasting unknown address data, etc.

FIG. 2 illustrates an embodiment of a VPLS 200 in a Multiprotocol LabelSwitching (MPLS) network domain 210. The MPLS network domain 210 may beone of a plurality of domains in an MPLS network. The VPLS 200 mayemulate an E-LAN functionality in standard Ethernet networks amongcustomer edge (CE) devices, such as a Layer 2 Virtual Private Network(L2VPN) service that provides multipoint-to-multipoint connectivity forEthernet across an Internet Protocol (IP) or an MPLS-enabled IP packetswitched network. The emulated E-LAN functionality may be achieved inthe MPLS network domain 210 as described in the Internet EngineeringTask Force (IETF) Request for Comments (RFC) 4761 and RFC 4762, whichare incorporated herein by reference.

The MPLS network domain 210 may comprise a plurality of PEs 216 that mayeach comprise a corresponding VSI. Each pair of VSIs in the PEs 216 maybe coupled together via a PW, which may be used to transport framesbetween the VSIs. The VSIs also may be coupled to one or more CEs 218(e.g. CE1, CE2, CE3, CE4, CE5, and CE6). The CEs 218 may be locatedoutside the MPLS network domain 210, such as in one or more separatenetworks or domains and/or at customer sites. Each VSI may be coupled toone or more CEs 218 via an Ethernet interface or a virtual Ethernetinterface, referred to herein as an attachment circuit (AC). The ACs maybe used to transport Ethernet frames between the VSIs and thecorresponding CEs 218.

The PEs 216 (and/or PEs in FIG. 1 ) may be network nodes, devices, orcomponents that support transportation of frames and/or packets throughthe MPLS network domain 210 (and/or the Ethernet bridged network domain110 of FIG. 1 ). For example, the PEs 216 may include bridges, switches,routers, or various combinations of such devices. The PEs 216 maycomprise a plurality of ingress ports for receiving frames and/orpackets from other nodes, logic circuitry that determines which nodes tosend the frames and/or packets to, and a plurality of egress ports fortransmitting frames and/or packets to the other nodes. In an embodiment,the PEs 216 may be label edge routers (LERs) that are configured to addor remove the labels of the frames and/or packets transported betweenthe MPLS network domain 210 and external networks. The CEs 218 may benetwork nodes, devices, or components configured similar to the PEs 216,but may be located outside the MPLS network domain 210. For instance,the CEs 218 may be customer sites or devices or may be coupled tocustomer sites or devices.

The VPLS 200 and the MPLS network domain 210 may support an E-Treeservice to transfer frames over the PWs between the VSIs, for instanceusing MAC-based forwarding. Some solutions for supporting E-Treeservices in MPLS/VPLS based networks have been proposed to the IETFPseudowire Emulation Edge to Edge version 3 (PWE3) workgroup (WG) andthe L2VPN WG, such as discussed in the IETF documentsdraft-key-12vpn-etree-frwk-04 (E-Tree-Frwk),draft-key-12vpn-vpls-etree-02 (VPLS-E-Tree), anddraft-simon-pwe3-cw-bit-01 (CW-LBit), all of which are incorporatedherein by reference.

FIG. 3 illustrates another embodiment of a VPLS based E-Tree 300 in anMPLS network domain 310. The MPLS network domain 310 may comprise aplurality of PEs 316 that may each comprise a corresponding VSI. Eachpair of VSIs in the PEs 216 may be coupled together via a PW, which maybe used to transport frames between the pair of VSIs. The VSIs also maybe coupled to one or more CEs 318 (e.g. CE1, CE2, CE3, CE4, CE5, andCE6), which may be located outside the MPLS network domain 310. Each VSIalso may be coupled to one or more CEs 218 via an Ethernet interface ora virtual Ethernet Interface (e.g. an AC), which may be used totransport Ethernet frames between the VSIs and the corresponding CEs218. The PEs 316 and the CEs 318 may be configured similar to the PEs216 and the CEs 218 of FIG. 2 , respectively.

The CEs 318 may be associated with the VPLS based E-Tree 300, where eachof the CEs 318 may be a root CE (represented by a rectangle) or a leafCE (represented by an oval). A root CE coupled to a first PE 316 mayexchange data frames with another root CE and/or a leaf CE coupled to asecond PE 316 via a corresponding PW and corresponding ACs. A first VSIin the first PE 316 may comprise a root end point (e.g. a first rootport at the first PE 316) that is coupled to a root CE 318. The firstVSI also may be coupled to a second VSI at the second PE 316 thatcomprises another root end point (e.g. a second root port at the secondPE 316), a leaf end point (e.g. a leaf port at the second PE 316), orboth. For example, CE1 may be a root CE that exchanges packets or frameswith another root CE, CE3, and with any one of the leaf CEs, CE4, CE5,and CE6. Similarly, CE3 may be another root CE that exchanges rootEthernet packets with CE1 and with any one of CEs, CE4, CE5, and CE6. Aleaf CE coupled to a first PE 316 may exchange data frames with a rootCE coupled to a second PE 316, but not with another leaf CE. Forexample, CE2 may be a leaf CE that exchanges packets or frames with CE3only, but not with CE4, CE5, and CE6. Similarly, each one of CE4, CE5,and CE6 may exchange data frames with CE1, CE2, and/or CE3 but not withthe other leaf CEs.

In FIG. 3 , the frames sent from the root CEs are indicated as rootEthernet frames (R-EP), and the frames sent from the leaf CEs areindicated as leaf Ethernet frames (L-EP). Each of the PEs 316 may beconfigured with a root or leaf attribute. As such, the PEs 316 or theVSIs at the PEs 316 may receive the frames from the CEs 318 and adddifferent tags to the frames before forwarding the frames to other PEs316. APE 316 may be a root PE that adds root tags to the frames sentfrom a root CE or may be a leaf PE that adds leaf tags to the framessent from a leaf CE before forwarding the frames to other PEs 316. Thetags in the frames may allow the other PEs 316 to differentiate betweenthe frames sent from root CEs and the frames sent from leaf CEs. Thus,the tags in the frames allow the PEs 316 to forward the frames properlyaccording to the E-Tree service rules and according to the MAC addressesin the frames. The PEs 316 also may remove the tags from the framesbefore forwarding the frames to the destination CEs (root or leaf CEs).

In some scenarios, the E-Tree service in the MPLS network domain 310 mayextend across multiple domains or networks, which may be coupled to oneanother, such as the MPLS network domain 210 of FIG. 2 , the EthernetBridged Network 110 of FIG. 1 , and/or other networks or domains. Toimplement the E-Tree services in each of the domains or networks, onedomain may use an IEEE 802.1 scheme and another domain may use an IETFMPLS/VPLS scheme. For example, the E-Tree service may be implemented inan MPLS network domain similar to the VPLS based E-Tree 300 and in anMEN coupled to the MPLS network domain similar to the E-Tree service100.

The domains and/or networks may be coupled to each other via one or morenetwork to network interfaces (NNIs), where each NNI may comprise twoend points at two coupled domains or networks. Implementing the E-Treeservice rules at the NNIs between the different networks or domains maybe difficult since the root and leaf attributes may not be supported atthe NNI's end points between the domains. Typically, an end point of theNNI (e.g. a first PE) at a first domain may remove the root or leaf tagbefore forwarding the frame to a second domain, e.g. at an externalnetwork. When the forwarded frame arrives at the other end point (e.g. asecond PE) of the NNI, the other end point may not be able to determinewhether the frame is sent from a leaf or root source. Thus, the framemay not be forwarded properly using the E-Tree service at the seconddomain.

Disclosed herein is a system and method for supporting an E-Tree serviceacross multiple networks or domains. The system may comprise an NNI endpoint configured to support root and leaf attributes across the domainsor networks. The end point may be associated with an E-Tree service thatextends the domains and may be configured with a trunk attribute. Thetrunk end point may be a PE that is used for interconnecting two similaror different domains, such as an MEN and MPLS/VPLS network domain. Thetrunk end point may translate the root and leaf tags in the framesbefore forwarding the frames and/or after receiving frames via an NNI.Thus, the PEs at a destination domain may be able to distinguish whetherthe frames are sent from a root or leaf source, and may properly forwardthe frames in the E-Tree service at the destination domain. Alsodisclosed is a system that supports an E-Tree service in a H-VPLSconfiguration. The system may comprise a bridge capable device that isconfigured with a trunk attribute similar to a trunk end point in theNNI.

FIG. 4 illustrates an embodiment of an E-Tree service 400 across aplurality of network domains. For instance, the E-Tree service 400 mayextend across a first MPLS network domain 410, a second MPLS networkdomain 420, and an MEN 430. The first MPLS network domain 410 may becoupled to the second MPLS network domain 420 via a first NNI, and thesecond MPLS network domain 420 may be coupled to the MEN 430 via asecond NNI. Each one of the first MPLS network domain 410, second MPLSnetwork domain 420, and MEN 430 may comprise a plurality of PEs (notshown) that may be coupled to a plurality of root CEs 412 and/or leafCEs 414. The PEs coupled to the root CEs 412 may have root attributes(represented by filled circles and referred to as root PEs), and the PEscoupled to the leaf CEs 414 may have leaf attributes (represented byhollow circles and referred to as leaf PEs). Each NNI also may comprisetwo end points 440, e.g. PEs, which may have trunk attributes.

Since each domain may use different tags to represent root frames andleaf frames within the domain, at least one trunk end point 440 for eachNNI may be configured to perform tag mapping or translation between thetwo corresponding domains. The trunk end point 440 may be aware of theroot and leaf tags used in the ingress domain and the root and leaf tagsused at the NNI or the egress domain. For instance, when the trunk endpoint 440 receives a frame from the ingress domain, the trunk end point440 may detect the tag in the frame. If the tag is a root tag, then thetrunk end point 440 may remove the root tag from the frame and addanother root tag that is used at the NNI before forwarding the frame viathe NNI. If the tag is a leaf tag, then the trunk end point 440 mayremove the leaf tag from the frame and add another leaf tag that is usedat the NNI before forwarding the frame via the NNI. When thecorresponding trunk end point 440 at the other end of the NNI receivesthe frame, the receiving trunk end point 440 may remove the root tag orleaf tag that is used at the NNI and add a corresponding root tag orleaf tag that is used at the egress domain. Thus, the PEs or nodes inthe egress domain may recognize the root or leaf tag in the frame andforward the frame properly in the egress domain using the E-Tree service400.

Mapping the domain's root and leaf tags into the NNI's root and leaftags may allow each of the domains associated with the NNI to use thedomain's own root and leaf tags without sharing the root and leaf taginformation with the other domain, which improves network security. TheNNI's root and leaf tags may be independent and different from the rootand leaf tags used in the ingress and egress domains. In otherembodiments, the NNI's root and leaf tags also may be used in theingress domain or the egress domain. For instance, one or both trunk endpoints 440 may perform tag translation on ingress traffic, e.g. beforeforwarding a frame to an egress domain, on egress traffic, e.g. afterreceiving a frame from an ingress domain, or both. Alternatively, bothtrunk end points 440 may perform tag translation on ingress traffic onlyor egress traffic only.

In some cases where a domain comprises only leaf end points or leaf CEs414 and is coupled to a single domain via a single NNI, such as the MEN430, the trunk end point 440 at the domain may perform trafficoptimization by not allowing frames that comprise leaf tags onto thedomain. Thus, leaf-to-leaf communications may be prevented in the E-Treeservice 400. The leaf tagged frames may be blocked at the trunk endpoint 440 at the egress domain (e.g. the MEN 430) or at thecorresponding trunk end point 440 at the ingress domain (e.g. the secondMPLS network domain 420). In the case where a domain comprises only leafCEs 414 and is coupled to a plurality of domains via a plurality ofNNIs, such as the second MPLS network domain 420, the trunk end point440 at the domain may allow frames that comprise leaf tags onto thedomain. The leaf tagged frames may be allowed to pass through the domainand may then be delivered to a destination domain that comprises a rootCE 412 (e.g. the MEN 430). The trunk end point 440 may use a signalingprotocol to inform other PEs in the domain to pass through the leaftagged frames.

Additionally, the trunk end point 440 may be configured to translate thedata information in the frames between the two associated domains sinceeach domain may use a different transport technology, such as the secondMPLS network domain 420 and the MEN 430. For example, the trunk endpoint 440 may be configured by the operator to properly decapsulate andencapsulate the data in the frames between the two domains whileforwarding the frames using the same E-Tree service across the domains.If the trunk end point 440 receives a frame that comprises an unknowntag, e.g. that is not recognized as a root or leaf tag, then the trunkend point 440 may discard the frame and inform the operator. In anotherembodiment, an edge router or a PE may be directly coupled to twodomains or networks, e.g. instead of the NNI. Similar to the trunk endpoint 440, the edge router may be configured to perform tag translationin the frame between the two domains before forwarding the frame fromthe ingress domain to the egress domain.

When an E-Tree spans across multiple domains, each domain may usedifferent tags to indicate root tagged frames and leaf tagged frames, asdescribed above. If two domains belong to the same operator, LabelDistribution Protocol (LDP) signaling or Border Gateway Protocol (BGP)signaling may be used to exchange the root and leaf tag informationbetween the two domains, and hence negotiate which trunk end point(s)may be used for tag translation. FIG. 5 illustrates one embodiment of anE-Tree service 500 across multiple domains. The E-Tree service 500 mayextend across a first MPLS network domain 510 and a second MPLS networkdomain 520, which may be coupled to each other via a switching PE (S-PE)540. The S-PE 540 may comprise a trunk end point at each of the twodomains, which may be configured similar to the trunk end pointsdescribed above. Each one of the first MPLS network domain 510 and thesecond MPLS network domain 520 may comprise a plurality of terminatingPEs (T-PEs) 511 (e.g. T-PE1, T-PE2, T-PE3, and T-PE4) that may becoupled to a plurality of root CEs 512 and/or leaf CEs 514. The T-PEs511 coupled to the root CEs 512 may have root attributes (represented byfilled circles and referred to as root PEs), and the T-PEs 511 coupledto the leaf CEs 514 may have leaf attributes (represented by hollowcircles and referred to as leaf PEs). Some of the T-PEs 511 may only becoupled to leaf CEs 514, such as T-PE2 and T-PE4.

Each MPLS domain may use different tags to represent the root taggedframes and the leaf tagged frames. Thus, the S-PE 540 may perform tagtranslation in the frame forwarding process between the two domains.When using LDP to configure the E-Tree service 500, each domain maysignal its tags to the S-PE 540, which may then perform tag translationat the data plane. When using BGP, a router reflector (not shown) may beused at the S-PE 540 according to RFC 4456, which is incorporated hereinby reference. The router reflector (RR) may be configured to receive theroot and leaf tag information from a first T-PE 511 in one domain, e.g.T-PE1, and may then pass the same tag values to a second T-PE 511, e.g.T-PE3, in the other domain. Alternatively, the RR may change the tagvalues before sending the tag information to the second T-PE 511. Inthis case, the S-PE 540 may perform tag translation in the frameforwarding process between the two domains.

FIG. 6 illustrates another embodiment of an E-Tree service 600 acrossmultiple domains. The E-Tree service 600 may extend across a first MPLSAutonomous System (AS) domain 610 and a second MPLS AS domain 620, whichmay be coupled to each other via an external interface. Each of thefirst MPLS AS domain 610 and the second MPLS AS domain 620 may comprisea plurality of PEs 611 (e.g. PE1, PE2, PE3, and PE4) that may be coupledto a plurality of root CEs 612 and/or leaf CEs 614. The PEs 611 coupledto the root CEs 612 may have root attributes (represented by filledcircles and referred to as root PEs), and the PEs 611 coupled to theleaf CEs 614 may have leaf attributes (represented by hollow circles andreferred to as leaf PEs). Some of the PEs 611 may only be coupled toleaf CEs 614, such as PE2 and PE4. Each of the first MPLS AS domain 610and the second MPLS AS domain 620 also may comprise an Autonomous SystemBoundary Router (ASBR) 640.

The ASBRs 640 may be coupled to each other to establish a trunk betweenthe two domains. As such, each ASBR 640 may be a trunk end point onopposite sides and may be configured similar to the trunk end pointsabove. The ASBRs 640 may use external BGP (EBGP) to communicate the rootand leaf tags between each other and perform tag translation during theframe forwarding process. If a PE 611 is only coupled to leaf CEs 614 inone domain, such as PE2 or PE4, the ASBR 640 in the domain may informthe second ASBR 640 in the second domain about the PE 611 status. Thus,the second ASBR 640 may not forward from the second domain any leaftagged frames that are destined to that PE 611, which may save networkresources.

A tag translation scheme similar to the tag translation scheme forE-Tree services across multiple domains may be implemented in an H-VPLSconfiguration, where a PE in a network domain may be coupled to aplurality of CEs via a switching device. FIG. 7 illustrates anembodiment of an H-VPLS configuration 700 that uses a bridge capabledevice, such as a Multi-Tenant Unit switch (MTU-s). The H-VPLSconfiguration 700 may comprise a plurality of PEs 712 that may belocated in the same domain (e.g. an MPLS network domain) and an MTU-s718 that may be coupled to one of the PEs 712, e.g. outside the domain.Each of the PEs 712 and the MTU-s 718 may comprise a VSI that may beassociated with the same E-Tree service. Each pair of PEs 712 may becoupled to each other via a PW, referred to herein as a hub PW, and theMTU-s 718 may be coupled to one of the PEs 712 via an additional PW,referred to herein as a spoke PW. The H-VPLS configuration 700 also maycomprise a plurality of CEs 716 that may be coupled to the MTU-s 718 viaan AC, such as CE1, or via an aggregate node 740 and multiple ACs, suchas CE2 and CE3.

The MTU-s 718 may be a bridge capable device that is configured todistinguish between the root tagged frames and the leaf tagged framesfrom the CEs 716, process the tags in the frames, and forward the framesaccordingly via the spoke PW. The MTU-s 718 also may receive leaf taggedframes and root tagged frames from the PE 712 via the spoke PW, processthe frames, and forward the frames to the destination CEs 716 accordingto the MAC addresses in the frames. The spoke PW between the PE 712 andthe MTU-s 718 may be configured as an intra NNI, where a first trunk endpoint may be located at the PE 712 and a second trunk end point may belocated at the MTU-s 718. The first and second trunk end points may beconfigured similar to the trunk end point 440 of FIG. 4 , and as suchmay perform tag translation in the frames forwarded between the PE 712and the CEs 716 as described above. If the PEs' domain (e.g. MPLSnetwork domain) and the MTU-s 718 use the same tagging scheme (same rootand leaf tags), then the trunk end points may not need to perform tagtranslation to forward the frames between the CEs 716 and the PEs 712.

In some embodiments, the multi domain E-Tree service model or the H-VPLSmodel may be implemented on one provider edge device, e.g. a PE. In thiscase, a Multi-Tenant Unit (MTU) module may reside on the PE.Additionally, the PE may be coupled to a peer PE that comprises a secondMTU module. The PE and similarly the peer PE may comprise a CustomerVLAN (C-VLAN) bridge and a Service VLAN (S-VLAN) bridge (that correspondto the MTU module) and a VSI, and may be coupled to a plurality ofroots, leaves, or both. The PE and the peer PE may be coupled via a PWthat serves as a trunk link between the two PEs. Each MTU module mayhave one trunk end point. The MTU modules on the different PEs may usedifferent tag values for root and leaf frame indication. As such, thetag translation described above may be implemented on each PE. Forinstance, if a frame with a remote VLAN leaf tag is received at the PEor the peer PE via the PW, then the remote VLAN leaf tag is mapped to alocal VLAN leaf tag. Similarly, if a frame with a remote VLAN root tagis received at the PE or the peer PE via the PW, then the remote VLANroot tag is mapped to a local VLAN root tag. In other words, at the PEwhere a frame exits the PW, if a frame with the remote leaf tag isreceived, then it is mapped to the local leaf tag; otherwise, if a framewith the remote root tag is received, then it is mapped to the localroot tag, wherein packets over both remote and local VLANs are processedin the same customer MAC space and are further forwarded or dropped inthe exit bridge module using the mechanism as described in IEEE 802.1Q.

FIG. 8 illustrates another embodiment of an H-VPLS configuration 800that does not use a bridge capable device on the customer side. TheH-VPLS configuration 800 may comprise a plurality of PEs 812 that may belocated in the same domain, e.g. in a core service network, and a PEswitch (PE-s) 818 that may be coupled to one of the PEs 812 outside thedomain. Each of the PEs 812 may comprise a VSI that may be associatedwith the same E-Tree service. Each pair of PEs 812 may be coupled toeach other via a hub PW and the PE-s 818 may be coupled to one of thePEs 812 via one or more spoke PWs. The H-VPLS configuration 800 also maycomprise a plurality of CEs 816 that may be coupled to the PE-s 818directly, such as CE1, or via an aggregate node 840, such as CE2 andCE3.

The PE-s 818 may be a Layer 2 switch that is configured to extend aspoke PW from each port coupled to a CE 816 or the aggregate node 840 toone PE 812 in the core service network. The ports at the PE-s 818 may becoupled to the CE 816 and the aggregate node 840 via corresponding ACs.The PE 812 may be a bridging VPLS PE router that forwards traffic overthe hub PWs, e.g. using MAC-based forwarding. Accordingly, each CE 816or aggregate node 840 may be coupled to the VSI in the PE 812 via acorresponding spoke PW, where the data frames may be transported withoutlearning or replication at the PE-s 818. For instance, the PE-s 818 mayforward the traffic received on the ACs and the corresponding ports tothe corresponding spoke PWs without processing. Similarly, the PE-s 818may forward the traffic received on the spoke PWs to the correspondingports and ACs without processing. To support the E-tree service, thespoke PW associated with each port may be assigned a root attribute(associated with a root AC) or a leaf attribute (associated with a leafAC). Thus, the PE 812 coupled to the spoke PWs may distinguish betweenthe frames sent from a root source or a leaf source and forward theframes properly in the domain using the E-Tree service.

In the schemes above, a PE may need to detect the frames received on anNNI or a spoke PW and perform tag addition to the frames beforeforwarding the frames to other PEs. The PEs also may need to announceits capability to perform E-Tree functions to the other PEs or nodes toensure proper forwarding of the frames in the E-Tree service. Forinstance, the PEs may announce E-Tree capability via LDP signaling asdefined in RFC 5561, BGP signaling as defined in RFC 5492, both of whichare incorporated herein by reference, or other signaling protocol usinga capability parameter TLV.

FIG. 9 illustrates an embodiment of a capability parameter TLV 900 thatmay be used in the LDP signaling protocol, the BGP signaling protocol,or other signaling protocols. For instance, a PE may advertise thecapability parameter TLV 900 in an LDP Initialization message to otherPEs to indicate whether the PE supports the procedures for E-Tree setup.The PE may advertise its E-Tree capability explicitly by sending thecapability parameter TLV 900 to the other PEs and indicating in thecapability parameter TLV 900 whether the PE supports the E-Treecapability or does not support the E-Tree capability. If a PE does notsupport E-Tree capability, the PE may only connect to a root CE andignore the signal message from a remote PE. The remote PE that supportsE-Tree capability and does not receive an E-Tree capability message froma peer PE may remove the tag from a received frame before sending theframe to the PE that does not support E-Tree capability. In anotherembodiment, the PE may advertise the capability parameter TLV 900explicitly or implicitly in a BGP Capabilities Optional Parameter asdefined in section 4 of RFC 5492.

The capability parameter TLV 900 may comprise an E-Tree capability field906, a Length field 908, and a reserved field 912. The E-Tree capabilityfield 906 may comprise a capability code that may be set to indicatethat the PE supports the E-Tree capability or may not be set if the PEdoes not support the E-Tree capability. The capability code may beassigned by the Internet Assigned Numbers Authority (TANA). The Lengthfield 908 may indicate the length of the capability parameter TLV 900,e.g. in bytes. The Reserved field 912 may be reserved and may not beused. The capability parameter TLV 900 also may comprise a first bit 902that may be set to about one (e.g. to indicate unknown), a second bit904 that may be set to about zero (e.g. to indicate non transitive), anda third bit 910 that may be set to about one to indicate E-Tree supportor to about zero to indicate no E-Tree support.

FIG. 10 illustrates an embodiment of an FEC TLV 1000 that may be usedaccording to the LDP signaling protocol, e.g. to setup an MPLS LabelSwitched Path (LSP). The FEC TLV 1000 may be used to advertise an E-Tree(or MPLS) FEC element. The FEC TLV 1000 may comprise an E-Tree Typefield 1002, an Address Family field 1004, an Information (Info) Lengthfield 1006, an E-Tree Identifier (ID) field 1010, and an InterfaceParameter sub-TLV 1012. The E-Tree Type field 1002 may comprise a valuethat represents the type of the E-Tree and may have a length of about 15bits. The Address Family field 1004 may comprise a value from theADDRESS FAMILY NUMBER in RFC 3036, which is incorporated herein byreference, which encodes the address family for the E-Tree ID. TheAddress Family field 1004 may have a length of about two octets. TheE-Tree ID field 1010 may comprise an E-Tree ID value that represents anE-Tree service instance that may be differentiated from other services.The E-Tree ID may be used as a virtual tunnel index and may have alength of about 32 bits. To simplify configuration, a sub-LSP ID of aningress node may be used as part of the virtual tunnel for transport toan egress node. The Interface Parameter sub-TLV 1012 may be configuredas described in RFC 4447, which is incorporated herein by reference.

FIG. 11 illustrates an embodiment of a generic label TLV 1100 that maybe based on RFC 3036. A label switch router (LSR) may use the genericlabel TLV 1100 to encode labels for use on links for which the labelvalues may be independent of the underlying link technology. Examples ofsuch links include Point-to-Point Protocol (PPP) and Ethernet links. Thegeneric label TLV 1100 may comprise a Generic Label field 1106, a Lengthfield 1108, and a Label field 1110, which may be configured according toRFC 3036. The Label field 1110 may comprise a 20-bit number (label) in afour-octet field as specified in RFC 3036. The generic label TLV 1100also may comprise a first bit 1102 and a second bit 1104 that may bothbe set to about zero.

FIG. 12 illustrates an embodiment of a multi label TLV 1200 that may beused to support an E-Tree service, e.g. in the LDP signaling protocol.The multi label TLV 1200 may be used to bind an LSP to a plurality oflabels, which may each be associated with a corresponding attribute. Forthe E-Tree service, a PW may be associated with two PW labels: one forthe root tagged frames and one for the leaf tagged frames. An egress PEmay use the multi label TLV 1200 to indicate to an ingress PE a firstlabel that may be associated with root tagged frames and a second labelthat may be associated with leaf tagged frames. The multi label TLV 1200may comprise a first bit 1202, a second bit 1204, a multi Label field1206, and a Length field 1208, which may be configured similar to thecorresponding fields in the generic label TLV 1100.

Additionally, the multi label TLV 1200 may comprise a plurality of Labelfields 1210 and a plurality of corresponding Attribute (Attrbt) fields1212. Each Label field 1210 may comprise a 20-bit number (label) in afour-octet field as specified in RFC 3032. Each Attribute field 1212 maycomprise about twelve bits and indicate that the corresponding label inthe Label field 1210 has an attribute. Using bit based attributes mayprovide up to about 12 labels per an LSP. For an E-Tree service, themulti label TLV 1200 may comprise about two Label fields 1210 thatspecify an E-Tree: a root label and a leaf label. In this case, a firstAttribute field 1212 may comprise a first attribute value 0x8 that isassociated with a root tagged frame and a second Attribute field 1212may comprise a second attribute value 0x4 that is associated with a leaftagged frame. An ingress PE may add the root label on the framesreceived from a root end point and the leaf label on the frames receivedfrom a leaf end point. The root label and the leaf label may bepreviously suggested by an egress PE using the multi label TLV 1200. Inother embodiments, the quantity of the Label field 1210 that specifiesthe E-Tree in the multi label TLV 1200 may be extended to more than two.Code Points also may be used for attributes.

In the case of the BGP protocol, multiple labels may be supported forthe same prefix as described in RFC 3107, which is incorporated hereinby reference. However, the labels may not be associated with definedattributes. Thus, the four-bit attributes in the generic label TLV 1100also may be used in the BGP signaling protocol to indicate that a firstlabel is associated with root tagged frames and a second label isassociated with leaf tagged frames.

In some embodiments, a plurality of fields may be used in the frameheader to represent root and leaf tags. For example, a first VLAN tagmay be added to the frame header to indicate a root tagged frame and asecond VLAN tag may be added to indicate a leaf tagged frame. In thiscase, an LDP protocol sub-interface TLV, e.g. according to RFC 3036, maybe used to communicate root and leaf tags between the PEs. In anotherscenario, a BGP protocol non-transitive path attribute may be used tosignal root and leaf tags, e.g. according to RFC 4271, which isincorporated herein by reference. The path attribute may comprise atriplet <attribute type, attribute length, attribute value> of variablelength. Additionally, an Attribute Type Code may be assigned for E-Treetags. The root tag and the leaf tag may be added in a path attributevalue field and an attribute length may used to reflect the length ofthe attribute value. The BGP protocol non-transitive path attribute alsomay be used to signal a leaf only PE or a leaf only domain, which mayallow other PEs or domains to perform traffic optimization as describedabove.

FIG. 13 illustrates an embodiment of a frame forwarding method 1300,which may be implemented by an end point associated with an E-Treeservice. For example, the frame forwarding method 1300 may beimplemented by an end point 440 of FIG. 4 , the S-PE 540 of FIG. 5 , oran ASBR 640 of FIG. 6 in multiple domains scenarios or by the MTU-s 718of FIG. 7 in an H-VPLS configuration scenario. The end point may be atrunk end point that has a trunk attribute and configured to perform tagtranslation, for instance between two domains or between a PE and a CEor aggregate node (in an H-VPLS configuration).

The method 1300 may begin at block 1310, where a frame may be received.For example, in a multiple domain scenario, the end point 440 mayreceive a data frame from the first MPLS network domain 410 or thesecond MPLS network domain 420. In an H-VPLS configuration scenario, theMTU-s 718 may receive a data frame from a CE 716. The tag may be a roottag that indicates a root source (e.g. root CE 412) for the frame or aleaf tag that indicates a leaf source (e.g. leaf CE 414). At block 1330,the method 1300 may determine whether the tag in the frame is valid. Forinstance, the tag may not be valid if the end point does not recognizethe tag as a root tag or a leaf tag. If the tag in the frame is valid,then the method 1300 may proceed to block 1340. Otherwise, the method1300 may proceed to block 1390.

At block 1340, the method may determine whether the tag in the frame isa root tag. If the tag is a root tag, then the method may proceed toblock 1350. Otherwise, the tag may be a leaf tag, and the method 1300may proceed to block 1360. At block 1350, the tag in the frame may betranslated. For instance, the tag may be translated if the frame'sdestination domain uses different root and leaf tags than the frame'ssource domain. In some cases, the end point also may translate theframe's data or encapsulate the frame if the frame's destination domainuses a different network technology than the frame's source domain. Atblock 1355, the frame may be forwarded. For example, the end point mayforward the frame from a first domain to a second destination domain orfrom an external CE to a PE in a network domain to the external CE.

At block 1360, the method 1300 may verify whether the frame'sdestination domain comprises a root end point. If the condition in block1360 is true, such as if the destination domain comprises only leaf endpoints, then the method 1300 may proceed to block 1350. Otherwise, themethod may proceed to block 1390. At block 1390, the frame may bediscarded, e.g. to prevent leaf-to-leaf communications in the E-Treeservice. The method 1300 may then end. In other embodiments, such aswhen the frame's source and destination domains use the same tags orwhen the forwarding end point is a switch that forwards leaf taggedframes and root tagged frames on separate PWs, the frame may beforwarded without processing the frame's tag and without tagtranslation.

FIG. 14 illustrates an embodiment of a transmitter/receiver unit 1400,which may be located at or coupled to any of the components describedabove. The transmitter/receiver unit 1400 may be any device thattransports data through the network. For instance, thetransmitter/receiver unit 1400 may correspond to or may be located in aPE, a CE, an end point, or any node described above. Thetransmitter/receiver unit 1400 may comprise a plurality of ingress portsor units 1410 for receiving frames, objects, or TLVs from other nodes,logic circuitry 1420 to determine which nodes to send the frames to, anda plurality of egress ports or units 1430 for transmitting frames to theother nodes.

The network components described above may be implemented on anygeneral-purpose network component, such as a computer or networkcomponent with sufficient processing power, memory resources, andnetwork throughput capability to handle the necessary workload placedupon it. FIG. 15 illustrates a typical, general-purpose networkcomponent 1500 suitable for implementing one or more embodiments of thecomponents disclosed herein. The network component 1500 includes aprocessor 1502 (which may be referred to as a central processor unit orCPU) that is in communication with memory devices including secondarystorage 1504, read only memory (ROM) 1506, random access memory (RAM)1508, input/output (I/O) devices 1510, and network connectivity devices1512. The processor 1502 may be implemented as one or more CPU chips, ormay be part of one or more application specific integrated circuits(ASICs) and/or digital signal processors (DSPs).

The secondary storage 1504 is typically comprised of one or more diskdrives or erasable programmable ROM (EPROM) and is used for non-volatilestorage of data. Secondary storage 1504 may be used to store programsthat are loaded into RAM 1508 when such programs are selected forexecution. The ROM 1506 is used to store instructions and perhaps datathat are read during program execution. ROM 1506 is a non-volatilememory device that typically has a small memory capacity relative to thelarger memory capacity of secondary storage 1504. The RAM 1508 is usedto store volatile data and perhaps to store instructions. Access to bothROM 1506 and RAM 1508 is typically faster than to secondary storage1504.

At least one embodiment is disclosed and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. Wherenumerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R₁, and an upper limit,R_(u), is disclosed, any number falling within the range is specificallydisclosed. In particular, the following numbers within the range arespecifically disclosed: R=R₁+k*(R_(u)−R₁), wherein k is a variableranging from 1 percent to 100 percent with a 1 percent increment, i.e.,k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97percent, 98 percent, 99 percent, or 100 percent. Moreover, any numericalrange defined by two R numbers as defined in the above is alsospecifically disclosed. Use of the term “optionally” with respect to anyelement of a claim means that the element is required, or alternatively,the element is not required, both alternatives being within the scope ofthe claim. Use of broader terms such as comprises, includes, and havingshould be understood to provide support for narrower terms such asconsisting of, consisting essentially of, and comprised substantiallyof. Accordingly, the scope of protection is not limited by thedescription set out above but is defined by the claims that follow, thatscope including all equivalents of the subject matter of the claims.Each and every claim is incorporated as further disclosure into thespecification and the claims are embodiment(s) of the presentdisclosure. The discussion of a reference in the disclosure is not anadmission that it is prior art, especially any reference that has apublication date after the priority date of this application. Thedisclosure of all patents, patent applications, and publications citedin the disclosure are hereby incorporated by reference, to the extentthat they provide exemplary, procedural, or other details supplementaryto the disclosure.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A method for forwarding an egress frame, themethod comprising: receiving, by a first trunk end point, a frame from anetwork domain, the frame comprising a first attribute value or a secondattribute value, wherein the first trunk end point and a second trunkend point are associated with an Ethernet-tree (E-Tree) service acrossthe network domain and a separate network domain, wherein the networkdomain and the separate network domain are coupled via a network tonetwork interface (NNI) including the first trunk end point and thesecond trunk end point, the first attribute value indicating that theframe originates from an end point having a root attribute of the E-Treeservice, the second attribute value indicating that the frame originatesfrom an end point having a leaf attribute of the E-Tree service;determining, by the first trunk end point, a first NNI value to beincluded in a NNI frame or a second NNI value to be included in the NNIframe, wherein the first NNI value is used at the NNI to indicate thatthe NNI frame originates from an end point having the root attribute ofthe E-Tree service, the second NNI value is used at the NNI to indicatethat the NNI frame originates from an end point having the leafattribute of the E-Tree service, the first NNI value is determinedaccording the first attribute value, and the second NNI value isdetermined according to the second attribute value; and transmitting, bythe first trunk end point subsequent to the determination, the NNI frameto the second trunk end point, wherein the second trunk end point isused to determine a third attribute value to be included in a secondframe or a fourth attribute value to be included in the second frame,wherein the third attribute value is used in the separate network domainto indicate that the second frame originates from an end point havingthe root attribute of the E-Tree service, the fourth attribute value isused in the separate network domain to indicate that the second frameoriginates from an end point having the leaf attribute of the E-Treeservice, the third attribute value is determined according the first NNIvalue, and the fourth attribute value is determined according to thesecond NNI value.
 2. The method of claim 1, wherein the first attributevalue differs from the first NNI value, the determining step comprises:mapping, by the first trunk end point, the first attribute value to thefirst NNI value.
 3. The method of claim 1, wherein the second attributevalue differs from the second NNI value, the determining step comprises:mapping, by the first trunk end point, the second attribute value to thesecond NNI value.
 4. The method of claim 1, wherein the first attributevalue is same as the first NNI value.
 5. The method of claim 1, whereinthe second attribute value is same as the second NNI value.
 6. Themethod of claim 1, wherein the third attribute value or the fourthattribute value are carried in a virtual local area network (VLAN) fieldin the second frame.
 7. The method of claim 1, wherein the thirdattribute value or the fourth attribute value are carried in a pathattributed value field in the second frame.
 8. The method of claim 1,wherein the first attribute value, the second attribute value, the firstNNI value, the second NNI value, the third attribute value, the forthattribute value are exchanged between the network domain and theseparate network domain based on Label Distribution Protocol (LDP)signaling or Border Gateway Protocol (BGP) signaling.
 9. A networkapparatus comprising: a first trunk end point associated with anEthernet-tree (E-Tree) service across a network domain and a separatenetwork domain, wherein the network domain and the separate networkdomain are coupled via a network to network interface (NNI) includingthe first trunk end point and a second trunk end point, and wherein thefirst trunk end point is configured to: receive a frame from the networkdomain, the frame comprising a first attribute value or a secondattribute value, the first attribute value indicating that the frameoriginates from an end point having a root attribute of the E-Treeservice, the second attribute value indicating that the frame originatesfrom an end point having a leaf attribute of the E-Tree service;determine, a first NNI value to be included in a NNI frame or a secondNNI value to be included in the NNI frame, wherein the first NNI valueis used at the NNI to indicate that the NNI frame originates from an endpoint having the root attribute of the E-Tree service, the second NNIvalue is used at the NNI to indicate that the NNI frame originates froman end point having the leaf attribute of the E-Tree service, the firstNNI value is determined according the first attribute value, and thesecond NNI value is determined according to the second attribute value;and transmit, subsequent to the determination, the NNI frame to thesecond trunk end point, wherein first NNI value is used by the secondtrunk end point to determine a third attribute value, and the second NNIvalue is used by the second trunk end point to determine a fourthattribute value, wherein the third attribute value is included in asecond frame and is used in the separate network domain to indicate thatthe second frame originates from an end point having the root attributeof the E-Tree service, and the fourth attribute value is included in asecond frame and is used in the separate network domain to indicate thatthe second frame originates from an end point having the leaf attributeof the E-Tree service.
 10. The network apparatus of claim 9, wherein thefirst attribute value differs from the first NNI value, the first trunkend point is configured to: map the first attribute value to the firstNNI value.
 11. The network apparatus of claim 9, wherein the secondattribute value differs from the second NNI value, the first trunk endpoint is configured to: map the second attribute value to the second NNIvalue.
 12. The network apparatus of claim 9, wherein the first attributevalue is same as the first NNI value.
 13. The network apparatus of claim9, wherein the second attribute value is same as the second NNI value.14. The network apparatus of claim 9, wherein the third attribute valueor the fourth attribute value are carried in a virtual local areanetwork (VLAN) field in the second frame.
 15. The network apparatus ofclaim 9, wherein the third attribute value or the fourth attribute valueare carried in a path attributed value field in the second frame. 16.The network apparatus of claim 9, wherein the first attribute value, thesecond attribute value, the first NNI value, the second NNI value, thethird attribute value, the forth attribute value are exchanged betweenthe network domain and the separate network domain based on LabelDistribution Protocol (LDP) signaling or Border Gateway Protocol (BGP)signaling.
 17. A network apparatus comprising: a second trunk end pointassociated with an Ethernet-tree (E-Tree) service across a networkdomain and a separate network domain, wherein the network domain and theseparate network domain are coupled via a network to network interface(NNI) including the second trunk end point and a first trunk end point,and wherein the second trunk end point is configured to: receive a NNIframe from the first trunk end point, the NNI frame comprising a firstNNI value or a second NNI value, wherein the first NNI value is used atthe NNI to indicate that the NNI frame originates from an end pointhaving the root attribute of the E-Tree service, and the second NNIvalue is used at the NNI to indicate that the NNI frame originates froman end point having the leaf attribute of the E-Tree service, whereinthe first NNI value is determined, by the first trunk end point,according to a first attribute value in a frame received by the firsttrunk end point from the network domain, and the second NNI value isdetermined, by the first trunk end point, according to a secondattribute value in the frame, wherein the first attribute valueindicating that the frame originates from an end point having a rootattribute of the E-Tree service, and the second attribute valueindicating that the frame originates from an end point having a leafattribute of the E-Tree service; determine, a third attribute value tobe included in a second frame or a fourth attribute value to be includedin the second frame, wherein the third attribute value is used in theseparate network domain to indicate that the second frame originatesfrom an end point having the root attribute of the E-Tree service, thefourth attribute value is used in the separate network domain toindicate that the second frame originates from an end point having theleaf attribute of the E-Tree service, the third attribute value isdetermined according the first NNI value, and the fourth attribute valueis determined according to the second NNI value; and transmit the secondframe to an endpoint associated with the E-tree service in the separatenetwork domain.
 18. The network apparatus of claim 17, wherein the firstNNI value differs from the third attribute value, the second trunk endpoint is configured to: map the first NNI value to the third attributevalue.
 19. The network apparatus of claim 17, wherein the second NNIvalue differs from the fourth attribute value, the second trunk endpoint is configured to: map the second NNI value to the fourth attributevalue.
 20. A method for forwarding an egress frame, the methodcomprising: receiving, by a second trunk end point, a NNI frame from afirst trunk end point, the NNI frame comprising a first NNI value or asecond NNI value, wherein the first trunk end point and the second trunkend point are associated with an Ethernet-tree (E-Tree) service across anetwork domain and a separate network domain, wherein the network domainand the separate network domain are coupled via a network to networkinterface (NNI) including the first trunk end point and the second trunkend point, wherein the first NNI value is used at the NNI to indicatethat the NNI frame originates from an end point having the rootattribute of the E-Tree service, the second NNI value is used at the NNIto indicate that the NNI frame originates from an end point having theleaf attribute of the E-Tree service, wherein the first NNI value isdetermined by the first trunk end point according a first attributevalue in a frame received by the first trunk end point from the networkdomain, and the second NNI value is determined by the first trunk endpoint according to a second attribute value in the frame, wherein thefirst attribute value indicating that the frame originates from an endpoint having a root attribute of the E-Tree service, the secondattribute value indicating that the frame originates from an end pointhaving a leaf attribute of the E-Tree service; determining, by a secondtrunk end point, a third attribute value to be included in a secondframe or a fourth attribute value to be included in the second frame,wherein the third attribute value is used in the separate network domainto indicate that the second frame originates from an end point havingthe root attribute of the E-Tree service, the fourth attribute value isused in the separate network domain to indicate that the second frameoriginates from an end point having the leaf attribute of the E-Treeservice, the third attribute value is determined according the first NNIvalue, and the fourth attribute value is determined according to thesecond NNI value; and transmiting the second frame to an endpointassociated with the E-tree service in the separate network domain. 21.The method of claim 20, wherein the first NNI value differs from thethird attribute value, the determining step comprises: mapping the firstNNI value to the third attribute value.
 22. The method of claim 20,wherein the second NNI value differs from the fourth attribute value,the determining step comprises: mapping the second NNI value to thefourth attribute value.
 23. A system comprising: a first trunk end pointand a second trunk end point associated with an Ethernet-tree (E-Tree)service across a network domain and a separate network domain, whereinthe network domain and the separate network domain are coupled via anetwork to network interface (NNI) including the first trunk end pointand the second trunk end point, wherein the first trunk end point isconfigured to: receive a frame from the network domain, the framecomprising a first attribute value or a second attribute value, thefirst attribute value indicating that the frame originates from an endpoint having a root attribute of the E-Tree service, the secondattribute value indicating that the frame originates from an end pointhaving a leaf attribute of the E-Tree service; determine, a first NNIvalue to be included in a NNI frame or a second NNI value to be includedin the NNI frame, wherein the first NNI value is used at the NNI toindicate that the NNI frame originates from an end point having the rootattribute of the E-Tree service, the second NNI value is used at the NNIto indicate that the NNI frame originates from an end point having theleaf attribute of the E-Tree service, the first NNI value is determinedaccording the first attribute value, and the second NNI value isdetermined according to the second attribute value; and transmit the NNIframe to the second trunk end point; wherein the second trunk end pointis configured to: receive the NNI frame from the first trunk end point;determine, a third attribute value to be included in a second frame or afourth attribute value to be included in the second frame, wherein thethird attribute value is used in the separate network domain to indicatethat the second frame originates from an end point having the rootattribute of the E-Tree service, the fourth attribute value is used inthe separate network domain to indicate that the second frame originatesfrom an end point having the leaf attribute of the E-Tree service, thethird attribute value is determined according the first NNI value, andthe fourth attribute value is determined according to the second NNIvalue; and transmit the second frame to an endpoint associated with theE-tree service in the separate network domain.